Customer phones up panicking. She'd been playing around with her scanner, scanning some pictures in, and had decided to scan in a £50 note. At that point the program crashed with the message "This program has performed an illegal operation and will be shutdown".
Plenty more here:
http://www.uktechsupport.f9.co.uk/humour/things.htm
http://www.uktechsupport.f9.co.uk/humour/things2.htm
http://www.uktechsupport.f9.co.uk/humour/things3.htm
http://www.uktechsupport.f9.co.uk/humour/humidx.htm
(all supposedly real)